The present invention relates generally to electronic measurement systems, and more particularly, to a method and apparatus for controlling automatic measurement systems using real-time clocks and data buffers. Unlike conventional devices which rely upon a central computer to issue complex interrupts and messages that command an instrument to gather and dispatch data to and from a device under test, the present invention utilizes a real-time clock and a data buffer to manage the process autonomously and simplify the entire measurement operation. Measurement system control using real-time clocks and data buffers provides an accurate, reliable, and cost effective method that can be used to coordinate the operation of a wide variety of diagnostic, stimulus, and monitoring instruments.
Complex instruments often require complicated coordination instructions from a central computer. When, for example, integrated circuits are fabricated in a chemical vapor deposition chamber, the temperature, pressure, and gaseous contents of the interior of the chamber are usually carefully regulated and monitored by a computer. This computer uses a program of instructions that contains many lines of software code to command actuators and valves to supply reactants to the chamber on a precise schedule.
The software code that is typically employed to provide the timing control for one or more instruments that gather data from or provide data to a device under test is generally tedious to compose, susceptible to errors, and often difficult to decipher by persons other than the author. The code is usually written in a simple programming language such as BASIC.
One problem created by using a central computer to manage the operation of one or many instruments via software utilizing interrupts or messages is the difficulty of making changes or improvements. Each time a new or different measurement or procedure is added, a voluminous listing of software instructions must be reviewed, rewritten, and re-entered into the memory of the central computer. Some additions or revisions may not be permitted by the constraints attributable to the hardware, network facility, or operating system that runs the applications programs on the computer. Other difficulties such as timing incompatibilities are encountered when the computer is modified or upgraded. If additional instruments are added to the system to make more measurements, the enlargement of the network can cause propagation delays that impair communications throughout the system. Another shortcoming of utilizing a central computer to handle all aspects of the operation of several instruments is the loss or confusion of output data. Once the computer has commanded the various instruments to collect information about an object or a device under test and the resulting instrument output signals are reported back to the central computer in accordance with its instructions, some data may arrive out of order or may be missing, and therefore ruin the measurements. Perhaps the greatest deficiency of present centralized timing control systems is their inefficient use of computer power. Since the central command computer must be intimately involved in the real-time control of the instruments and in dispatching data, the central computer remains in an unproductive waiting mode during a large segment of the operation.
The problem of providing a reliable and efficient measurement control system that avoids the shortcomings recited above has presented a major challenge to designers in the field of computer operated instrumentation systems. The development of a method and an apparatus that is flexible, easy to upgrade, allows for the addition of new instruments to an old network, and which better utilizes the resources of a control computer would constitute a major technological advance in the instrumentation business. The enhanced performance that could be achieved using such an innovative device would satisfy a long felt need within the industry and would enable both manufacturers and users of complex measurement devices to save substantial expenditures of time and money.